The present invention relates to image processing apparatus, and more particularly to an image processing apparatus which generates, through a pixel-skipping process, a pixel-reduced image from an original image.
In photolithographic printing, a pre-press proof is prepared by scanning a layout sheet to obtain its image information in data form. The so obtained is digitalized, whereby image correction, improvement, color adding, etc. processes may be carried out, during which the obtained image is displayed on a screen.
In order to facilitate image-processing, the on-screen image is "pixel-skipped" such that the display image is composed of a number of pixels less than that corresponding to the original, making the density of the obtained image suitable for the display, as well as for printing apparatus.
Conventionally, an image processing apparatus simply skips display image-generating pixels according to a pixel skipping ratio. However, this results in one side effect wherein dot and fine-line features of an image may disappear when the image undergoes the pixel-skipping process.
Japanese Patent Laying-Open No. 151877/1989 and Japanese Patent Laying-Open No. 152868/1989 disclose a technology which can solve the above problem of disappearing fine line features. Image processing apparatus as disclosed in the documents determine during a pixel-skipping process whether or not each pixel potentially to be skipped is isolated in color; in case an examined (objective) pixel is isolated, an adjacent pixel which is not isolated is skipped instead.
According to the foregoing technology, however, if the adjacent as well as the objective pixel is isolated, the adjacent pixel is nonetheless skipped. Consequently, dot and fine-line characteristics of the original image are degraded in the obtained image. In cases in which the skipping ratio is high, i.e., when a large number of pixels are skipped, the problem can become severe, because the number of pixels that are skipped may be larger than that of the remaining pixels forming the obtained image.